Major pathogens of fish and other farmed aquatic animals include bacteria, fungi, viruses and parasites. These can lead to serious infectious diseases and losses representing one of the major limitation to sustainable aquaculture. Routine health checks for key priority pathogens of tilapia, carp and catfish—will vary with geographies—are important to minimize the risk of their introduction, transmission and spread. On suspicion of an unknown disease during abnormal mortalities, it is routine for the investigators to collect clinical samples from moribund fish for molecular and virology diagnostics. Molecular diagnostics are techniques used to amplify small DNA/RNA sequence(s) that are unique to a particular pathogen to ascertain their presence or absence. Virology is a branch of microbiology that study viruses and viral diseases. WorldFish and partners developed this quick fish sampling guide for molecular and virology diagnostics. Standard specimens for general molecular and virology health evaluation include kidney, liver, spleen, brain and gills. Other tissues may be collected.

During investigation of an abnormal mortality event, fish tissues (or biopsies) for histopathology analysis are collected for disease diagnosis. Histology consists in the preparation of thin, stained tissue sections for microscopic examination to study their structure and function. Histopathology is the study of disease and disease processes by looking at the change in the anatomy or anomalies from cells, tissues and organs as seen through a microscope. WorldFish and partners developed this quick fish-sampling guide for histology. Standard biopsy specimens for histological examination consists of fixed sections of brain, gill, heart, intestine, kidney, liver and spleen. Other tissues may be collected in the presence of external lesions/ulcers (e.g., eye, skin, muscle). A free online training course on histology sampling is also available via Learn.ink.